Mushroom cloud explosion captured on video after oil train derails

Camera crews in the US have unexpectedly filmed the moment an oil train exploded "like a mushroom cloud" after it derailed, spilling into a river and causing the evacuation of a town.

The WSAZ interview was cut short when the derailed train being discussed started to catch on fire before suddenly exploding in the eastern US state of West Virginia at 1.20pm local time today.

"We were standing on the river bank when we saw the train explode … it shot up a mushroom cloud about as high as it is now," a man who witnessed the crash tells the media, as the trains bursts into flames once again.

Roaring spirals of fire and black smoke plume from the burning wreckage as the group, although several blocks from the scene, take a few steps back.

"Man that's high," another man remarks off camera.

The train hauling crude oil from North Dakota careened off the rails in West Virginia and burst into flames as up to a dozen train cars exploded one by one.

Governor Earl Ray Tomblin declared a state of emergency for Kanawha and Fayette counties, so the affected areas can "have the access they need to resources necessary to handle all stages of the emergency."

No injuries were immediately reported.

Local CBS television affiliate WOWK said authorities had ordered the evacuation of the Powelltown Hollow area.

"State officials are on site and will continue to work with local and federal officials, as well as CSX representatives, throughout the incident," Tomblin said.

"Officials at the Montgomery and Cedar Grove water intakes continue to monitor the situation."